> -----Original Message----- > From: Marc Zyngier [mailto:marc.zyngier@xxxxxxx] > Sent: Monday, October 07, 2013 9:11 PM > To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx; > kvm@xxxxxxxxxxxxxxx > Subject: [PATCH 2/2] arm64: KVM: Yield CPU when vcpu executes a WFE > > On an (even slightly) oversubscribed system, spinlocks are quickly becoming a > bottleneck, as some vcpus are spinning, waiting for a lock to be released, while > the vcpu holding the lock may not be running at all. > > The solution is to trap blocking WFEs and tell KVM that we're now spinning. This > ensures that other vpus will get a scheduling boost, allowing the lock to be > released more quickly. > > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > --- > arch/arm64/include/asm/kvm_arm.h | 8 ++++++-- > arch/arm64/kvm/handle_exit.c | 18 +++++++++++++----- > 2 files changed, 19 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h > index a5f28e2..c98ef47 100644 > --- a/arch/arm64/include/asm/kvm_arm.h > +++ b/arch/arm64/include/asm/kvm_arm.h > @@ -63,6 +63,7 @@ > * TAC: Trap ACTLR > * TSC: Trap SMC > * TSW: Trap cache operations by set/way > + * TWE: Trap WFE > * TWI: Trap WFI > * TIDCP: Trap L2CTLR/L2ECTLR > * BSU_IS: Upgrade barriers to the inner shareable domain > @@ -72,8 +73,9 @@ > * FMO: Override CPSR.F and enable signaling with VF > * SWIO: Turn set/way invalidates into set/way clean+invalidate > */ > -#define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWI | HCR_VM | HCR_BSU_IS | \ > - HCR_FB | HCR_TAC | HCR_AMO | HCR_IMO | HCR_FMO | \ > +#define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \ > + HCR_BSU_IS | HCR_FB | HCR_TAC | \ > + HCR_AMO | HCR_IMO | HCR_FMO | \ > HCR_SWIO | HCR_TIDCP | HCR_RW) > #define HCR_VIRT_EXCP_MASK (HCR_VA | HCR_VI | HCR_VF) > > @@ -242,4 +244,6 @@ > > #define ESR_EL2_EC_xABT_xFSR_EXTABT 0x10 > > +#define ESR_EL2_EC_WFI_ISS_WFE (1 << 0) In another patch this is named as WHI_IS_WFE whereas here it is WFI_ISS_WFE, looks like typo. Anyways, what I am interested to understand is what does this macro means? Thanks -Bharat > + > #endif /* __ARM64_KVM_ARM_H__ */ > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index > 9beaca03..8da5606 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -47,21 +47,29 @@ static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run > *run) } > > /** > - * kvm_handle_wfi - handle a wait-for-interrupts instruction executed by a > guest > + * kvm_handle_wfx - handle a wait-for-interrupts or wait-for-event > + * instruction executed by a guest > + * > * @vcpu: the vcpu pointer > * > - * Simply call kvm_vcpu_block(), which will halt execution of > + * WFE: Yield the CPU and come back to this vcpu when the scheduler > + * decides to. > + * WFI: Simply call kvm_vcpu_block(), which will halt execution of > * world-switches and schedule other host processes until there is an > * incoming IRQ or FIQ to the VM. > */ > -static int kvm_handle_wfi(struct kvm_vcpu *vcpu, struct kvm_run *run) > +static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run) > { > - kvm_vcpu_block(vcpu); > + if (kvm_vcpu_get_hsr(vcpu) & ESR_EL2_EC_WFI_ISS_WFE) > + kvm_vcpu_on_spin(vcpu); > + else > + kvm_vcpu_block(vcpu); > + > return 1; > } > > static exit_handle_fn arm_exit_handlers[] = { > - [ESR_EL2_EC_WFI] = kvm_handle_wfi, > + [ESR_EL2_EC_WFI] = kvm_handle_wfx, > [ESR_EL2_EC_CP15_32] = kvm_handle_cp15_32, > [ESR_EL2_EC_CP15_64] = kvm_handle_cp15_64, > [ESR_EL2_EC_CP14_MR] = kvm_handle_cp14_access, > -- > 1.8.2.3 > > > > _______________________________________________ > kvmarm mailing list > kvmarm@xxxxxxxxxxxxxxxxxxxxx > https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
